1. Field of the Invention
The present invention relates to a vehicle driving force control apparatus for a four-wheel drive vehicle capable of driving the main drive wheels by an internal combustion engine, and driving the subordinate drive wheels by an electric motor. More particularly, the present invention relates to a driving force control apparatus for a so-called batteryless four-wheel drive vehicle where the internal combustion engine drives a generator that supplies the generated electric power to the electric motor.
2. Background Information
An example of a driving force control apparatus for a batteryless four-wheel drive vehicle is disclosed in Japanese Laid-Open Patent Application No. 2000-318472. The driving force control apparatus of this publication is constituted so that, in a range below a predetermined traveling speed set to, for example, approximately 15 km/h, an electric motor is driven when the speed differential between the front and rear wheels reaches or exceeds a predetermined value, i.e., when the acceleration slippage reaches or exceeds a predetermined value. The electric motor is driven in accordance with an accelerator position opening degree. For example, when the accelerator position opening degree is in a range greater than or equal to a predetermined value, a fixed distribution amount of the engine output is used as the driving force for the generator, and the electric power generated by that driving force is supplied to the electric motor, which drives the subordinate drive wheels.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved driving force control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.